Recommend a different command for missing loaders based on the presence of yarn/npm lock files

fixtures/package-helper/yarn-npm/yarn.lock

@@ -0,0 +1,2 @@
+# THIS IS AN AUTOGENERATED FILE. DO NOT EDIT THIS FILE DIRECTLY.
+# yarn lockfile v1

fixtures/package-helper/yarn/yarn.lock

@@ -0,0 +1,2 @@
+# THIS IS AN AUTOGENERATED FILE. DO NOT EDIT THIS FILE DIRECTLY.
+# yarn lockfile v1

lib/friendly-errors/formatters/missing-loader.js

@@ -32,7 +32,7 @@ function formatErrors(errors) {
             );
 
             if (packageRecommendations) {
-                fixes.push(`${packageRecommendations.message}\n              ${packageRecommendations.yarnInstall}`);
+                fixes.push(`${packageRecommendations.message}\n              ${packageRecommendations.installCommand}`);
             }
         } else {
             fixes.push('You may need to install and configure a special loader for this file type.');

lib/package-helper.js

@@ -10,6 +10,7 @@
 'use strict';
 
 const chalk = require('chalk');
+const fs = require('fs');
 
 function ensurePackagesExist(packageNames, requestedFeature) {
     const recommendation = getPackageRecommendations(packageNames, requestedFeature);
@@ -20,10 +21,21 @@ function ensurePackagesExist(packageNames, requestedFeature) {
 
     throw new Error(`
 ${recommendation.message}
-  ${recommendation.yarnInstall}
+  ${recommendation.installCommand}
 `);
 }
 
+function getInstallCommand(packages) {
+    const hasYarnLockfile = fs.existsSync('yarn.lock');
+    const hasNpmLockfile = fs.existsSync('package-lock.json');
+
+    if (hasNpmLockfile && !hasYarnLockfile) {
+        return chalk.yellow(`npm install ${packages.join(' ')} --save-dev`);
+    }
+
+    return chalk.yellow(`yarn add ${packages.join(' ')} --dev`);
+}
+
 function getPackageRecommendations(packageNames, requestedFeature = null) {
     let missingPackageNames = [];
 
@@ -48,11 +60,11 @@ function getPackageRecommendations(packageNames, requestedFeature = null) {
         message += ` to use ${chalk.green(requestedFeature)}`;
     }
 
-    let yarnInstall = chalk.yellow(`yarn add ${missingPackageNames.join(' ')} --dev`);
+    const installCommand = getInstallCommand(missingPackageNames);
 
     return {
         message,
-        yarnInstall
+        installCommand
     };
 }
 

test/package-helper.js

@@ -0,0 +1,49 @@
+/*
+ * This file is part of the Symfony Webpack Encore package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+'use strict';
+
+const expect = require('chai').expect;
+const packageHelper = require('../lib/package-helper');
+const path = require('path');
+const process = require('process');
+
+describe('package-helper', () => {
+    const baseCwd = process.cwd();
+
+    describe('recommended install command is based on the existing lock files', () => {
+        after(() => {
+            process.chdir(baseCwd);
+        });
+
+        it('missing packages without any lock file', () => {
+            process.chdir(path.join(__dirname , '../fixtures/package-helper/empty'));
+            const packageRecommendations = packageHelper.getPackageRecommendations(['foo', 'webpack', 'bar']);
+            expect(packageRecommendations.installCommand).to.contain('yarn add foo bar');
+        });
+
+        it('missing packages with package-lock.json only', () => {
+            process.chdir(path.join(__dirname, '../fixtures/package-helper/npm'));
+            const packageRecommendations = packageHelper.getPackageRecommendations(['foo', 'webpack', 'bar']);
+            expect(packageRecommendations.installCommand).to.contain('npm install foo bar');
+        });
+
+        it('missing packages with yarn.lock only', () => {
+            process.chdir(path.join(__dirname, '../fixtures/package-helper/yarn'));
+            const packageRecommendations = packageHelper.getPackageRecommendations(['foo', 'webpack', 'bar']);
+            expect(packageRecommendations.installCommand).to.contain('yarn add foo bar');
+        });
+
+        it('missing packages with both package-lock.json and yarn.lock', () => {
+            process.chdir(path.join(__dirname, '../fixtures/package-helper/yarn-npm'));
+            const packageRecommendations = packageHelper.getPackageRecommendations(['foo', 'webpack', 'bar']);
+            expect(packageRecommendations.installCommand).to.contain('yarn add foo bar');
+        });
+    });
+});